Many prior attempts have been made with limited success to design a convenient, effective and simple stop device which when mounted to one sash of a double-hung window permits limited opening of either or both sashes for ventilation. It is important, of course, for such a device to be mounted so as to be inaccessible to an outsider seeking entry, and in this sense the device serves to lock or prevent opening of the window beyond that permitted by the stop device.
U.S. Pat. Nos. 94,791; 1,047,191; 888,039; 928,339; 2,167,960; and 2,331,676 are illustrative and representative of prior attempts in this field. Each lacks the extreme simplicity of the present invention and none is completely satisfactory in function. Ideally, a ventilation stop should be able to be mounted quickly, easily and securely and thereafter should be able to be placed in operative and inoperative positions in a fool-proof manner. Additionally, it is desirable that the stop be able to secure the lower sash in the partially open position, that is, to hold it in this position. It is with respect to the foregoing aspects that the present invention has succeeded where prior attempts have only partially been successful, as will be now explained in greater detail.